Method and means of continuous casting of light metals



July 17, 1956 s. A. KILPATRICK METHOD AND MEANS OF' CONTINUOUS CASTING OF' LIGHT METALS Filed Sept. 3. 1952 3 Sheets-Sheet 1 INVENTOR.

:ETTORNE scm wily A. PATRICK July 17, 1956 s. A. KILPATRICK 2,754,556

METHOD AND MEANS OF CONTINUOUS CASTING OF LIGHT METALS Filed Sept. 5, 1952 3 Sheets-Sheet 2 l 54 14 C54 22 j 22 5 2 1 P V f N 11-- iff- #24 A' gs 21 i lO 2O ,l V/ Y 9 19 i I I. wy I l l? 1 I l I l I l I Y Y* l l i l1l IL l 5 l VI? E 1 l l L i i I a s l 1 l 15 k": ,1| L L FI G. 2.

IN VEN TOR. sTANL/EY A KILPBTRI GK ATTORNEY July 17, 1956 5 A, K|LpATR|K 2,754,556

METHOD AND MEANS 0F CONTINUOUS CASTING OF LIGHT METALS Filed Sept. 3, 1952 3 Sheets-Sheet 3 INVENTOR. STBNJ-JQY B' lLPTRlCH 6 JHTTORN United States Patent O METHOD AND MEANS F CONTINUOUS CASTING 0F LIGHT METALS Stanley A. Kilpatrick, Spokane, Wash., assigner to Kaiser Aluminum & Chemical Corporation, Oakland, Calif., a corporation of Delaware Application September 3, 1952, Serial No. 307,579

12 Claims. (Cl. 22-57 .2)

This invention relates to the continuous casting of light metals by the direct chill method. More particularly the invention relates to an improved method and apparatus for continuously casting high strength aluminum alloy ingots of relatively massive cross-section.

In the continuous casting of various metals including aluminum and aluminum alloys, molten metal is fed into an open-ended mold which is continuously cooled and wherein the molten metal is partially cooled in the mold to form an outer shell of solidified metal. The casting is continuously withdrawn by any suitable means from the opposite end while at the same time a supply of cooling fluid, usually water, continuously contacts the embryo casting as it emerges from the mold. The casting procedure may be a strictly continuous process (in which the casting is cut to length Without interruption of the casting procedure) or it may be semi-continuous; i. e., a casting of desired length may be cast, the flow ot metal stopped, the casting removed and the procedure commenced anew. Continuous casting as herein used refers to either type of operation. In the case of aluminum and aluminum alloys, one method commonly used is that disclosed in the Ennor Patent No. 2,301,027.

In the Ennor patent the cooling is accomplished by means of a water spray directed around the periphery of the mold shell by means of spray pipes or a spray box. Water jets impinge upon the outer surface of the mold and the embryo ingot as it emerges below the mold. The amount of water applied or the amount of cooling accomplished is uniform about the periphery of the mold and casting.

The desirability in continuous casting processes ot' maintaining relatively rapid freezing of the molten metal and avoidance of a deep molten crater in order to obtain good metallurgical quality are recognized by the prior casting art as evidenced by Ennor. The rapid freezing of the molten metal and the maintenance of a relatively shallow body of molten metal or molten metal crater is of particular importance in substantially reducing or eliminating a defect found in ingots of large cross-section commonly referred to as shrinkage porosity. Where the rate of solidilication of the ingot is relatively slow, the molten crater becomes relatively deep and generally assumes a V-shaped configuration. The metal material within the lower portion or at the base of the molten metal crater is generally of a mushy consistency and comprises solid particles mixed with molten metal. During the freezing or solidification of this material, there appears to be a tendency for pre-freezing and bridging to occur over the lowermost portion of the crater material. As solidiiication of this portion goes on to completion, the remaining molten metal in this portion solidities and contracts thus leaving a plurality of voids which are not subsequently filled by more molten metal from the molten crater above, due to the bridging or pre-freezing which has occurred.

While the application of coolant directly to the em- 2,754,556 Patented July 17, 1956 rice bryo ingot immediately upon emergence from below the bottom of a water-cooled mold sleeve of relatively short length has served to promote rapid freezing and to improve metallurgical quality considerably, the inherent characteristics of all prior process and/or devices designed to accomplish such cooling are conducive to center splits and edge cracks in ingots or billets of large cross-section and particularly in the case of high strength aluminum alloys such as 14S, 17S, 24S, 75S, etc., where in the ingot possesses a crosssectional configuration such as circular, square, or other polygonal shape.

lt is known that where the cooling rates or, in other words, the rate and/or extent of heat abstraction both during and after soliditication of large ingots is not closely controlled, there are set up in the ingots excessive internal stresses which generally will result in center splits, edge cracks and other serious defects. Such splits and cracks may occur during the actual casting operation. Other times these defects will become noticeable after the ingot has stood for a period of time after casting, while in yet other instances, the defects will occur during the subsequent machining of the ingot. These excessive stresses resulting in splits and cracks are in effect thermal stresses generated by overcooling the ingot after solidilication is complete. These defects of splitting and cracking render the ingots unsuitable for working or machining and thus result in considerable economic loss to the industry. Also these defects constitute a hazard.

This tendency of high strength aluminum alloy ingots to develop center splits and edge cracks has imposed limits on the sizes or cross-sectional areas which may be cast by means of conventional practices. For example, it has been impossible to cast satisfactory ingots on the order of 32 inches in diameter in alloys such as 14S, 17S, 24S and 75S. Moreover, this tendency toward center splits and edge cracks has made it impossible to obtain satisfactory results in casting ingots on the order of 18 by 18 inches square in alloys such as 24S and, in certain instances, such as S alloy, in casting ingots with cross-sectional dimensions as low as l2 by 12 inches square. As a consequence of this situation, the industry has labored under an extremely serious handicap in that it has not had available large ingots of a cross-section required for forging presses adapted to malte large or massive forgings of the type required by the aircraft industry.

It has been proposed that arrestment or diminution of the rates of cooling or, in other words, the rate and/or extent of heat abstraction of the ingots by effectively retrieving all or as much as is necessary of the coolant flowing down the ingot surface below the bottom of the mold shell such that the surface of the ingot will be maintained at a temperature not substantially below about 300 F., and preferably is from 400-600 F., below the level of coolant removal during the remainder of the casting operation that the incidence of center splits and edge cracks in ingots of relatively massive cross-section is considerably reduced. Also, it has been proposed that the coolant be removed from the ingot surface by means of jets which cause streams of gas to impinge upon the ingot surface in an upwardly directed angle to strip the coolant from the ingot surface. Alternatively, a mechanical wiper has been proposed wherein a synthetic rubber or neoprene ring-like member contacts and wipes the coolant from the ingot surface. Although by means of the above procedure it has been found possible to continuously cast sound ingots of relatively massive cross-section e. g., 32" in diameter, which was not possible by utilizing prior conventional practices, it has been found that in certain instances, depending upon the chemical composition and size of the alloy ingot being cast, that it is difficult to l? maintain consistently reproducible results except by extremely close control over the casting operation.

This invention embraces the discovery that by means of proper control and distribution of the molten metal ow to the mold shell and to the outer ingot shell of solidified metal, in addition to the above discussed control of the rate of heat abstraction, the disadvantages attendant in prior practices are overcome and consistently reproducible results can be attained with a minimum of control necessary. By means of the instant invention, this control and distribution of the molten metal to the ingot and mold shells is had by the use of a novel baille arrangement. Various baffle arrangements have been proposed in the prior art for controlling in some degree the distribution of metal within the mold shell but for one or more reasons none of these prior battles provide the necessary control as does the battle arrangement of this invention. Moreover, none of the prior art teachings indicate the critical relationship found to exist between metal distribution and the rate of heat abstraction from the ingot.

It has been found that proper distribution of the molten metal within the mold shell has a decided effect on the successful continuous casting of ingots of relatively large or massive cross-section. In the casting of these massive ingots, it has been determined that it is necessary to attain a sufficiently low drop rate to prevent the occurrence of center cracking and shrinkage porosity and at the same time also prevent the occurrence of pre-freezing of metal within the mold shell occasioned by too low a drop rate which causes a defect commonly known as a cold shut. In addition to the drop rate, it has also been found that the direction of How of the molten metal within the mold shell is an important factor in the successful casting of massive ingots. By means of the instant invention, the factors of rate of ilow of the molten metal together with the distribution of this metal within the mold shell have been so correlated and combined with the rate of heat abstraction as to give rise to a highly successful procedure for continuously casting sound, massive ingots with a minimum of control necessary.

Although the method of the instant invention has been found particularly adapted for use in the continuous casting of ingots of high strength aluminum alloys of relatively massive size, its use is not restricted thereto, and it can be advantageously employed in the continuous cast- 1ng of any metal where the danger of center splitting and other serious defects caused by improper control of metal distribution, rate of metal How, and excessive cooling of the ingot or billet exist.

Accordingly, it is an object of this invention to provide an improved method for continuously casting sound metal ingots of large cross-sectional areas heretofore not possible with conventional methods.

Another object is to provide an improved method for continuously casting ingots including the control of the rate of metal flow to the mold and the distribution of the metal within the mold to eliminate or substantially reduce the formation of center splits, cold shuts and other defects.

Another object is to provide a method for eliminating or substantially reducing center splitting, surface tears and other defects in various types of metal ingots, and particularly high strength aluminum alloy ingots of relatively massive cross-section, by proper metal distribution and cooling ofthe ingot as it is being cast.

A further object is to provide a novel method for continuously casting ingots whereby said ingots possess a minimum of segregation of alloying constituents, relatively small grain size and low shrinkage porosity.

A more specic object is to provide an improved method for continuously casting ingots of high strength aluminum alloys having a relatively massive cross-sectional area and characterized by being free of center splits, edge cracks, and cold shuts and possessing small grain structure, a relatively fine size and uniform distribution of constituents and a minimum of shrinkage porosity.

Another object is to provide an improved casting apparatus including a novel baffle means for controlling the rate of flow of metal to the mold shell and for controlling the direction of flow of said metal within the mold shell.

A further object is to provide a novel baille for controlling the rate and direction of How of metal within a mold.

In the process and apparatus of the invention, the rate and direction of flow of the molten metal is controlled by means of a baffle which may comprise a cup or bowlshaped container provided with a predetermined number of feed holes or apertures in the lower portion adjacent the base thereof. The battle is centered in the mold beneath the pouring spout with the lower portion of the baffle immersed in the molten metal crater or primary molten metal body contained in the mold shell. While the body of molten metal contained in the battle is positioned partially within the molten metal crater or primary molten metal body, the surface level of the molten metal body Within the baffle is maintained slightly above the surface level of the primary molten metal body in the mold shell. The feed holes or apertures provided adjacent the base of the baffle are of such size and in such position relative to the inner wall of the mold shell that the molten metal is caused to ow at a predetermined velocity laterally to the critical zone or zones of the inner wall of the mold and ingot shells thereby preventing the occurrence of pre-freezing or freezing back" of the metal with the possible defects of cold-shuts, surface tears or spill outs as well as eliminating any condition of an overly deep molten metal crater. Moreover, by means of the instant invention, the rate of How of the molten metal to the mold and ingot shells is controlled within predetermined limits for any given set of casting conditions whercby the drop rate of the ingot is such that control ot' shrinkage porosity and center cracks can be readily maintained. The determination of the size of the baille, the size and position of the feed holes or apertures, and the rate of molten metal ow can be readily accomplished for any given alloy size with a nominal amount of trial and error experimentation.

Further objects and advantages of the invention will be apparent from the following detailed description taken in conjunction with the drawings which illustrate various embodiments of apparatus for performing the method of the invention and wherein:

Figure 1 is a. broken plan view showing one form of continuous casting apparatus embodying the principle of the invention.

Figure 2 is a vertical, sectional view taken along lines 2-2 of Figure 1 on reduced size, the position assumed by the ingot as it is lowered from the mold being shown in dotted lines.

Figure 3 is a plan view showing in more detail one form of baille of the invention which can be used when casting square ingots as in Figures l and 2.

Figure 4 is a vertical, sectional view of the baffle taken along lines 4--4 of Figure 3.

Figure 5 is a plan view showing in detail one form of bale suitable for casting circular ingots.

Figure 6 is a vertical, sectional view taken along lines 6--6 of Figure 5.

With further reference to the drawings and particularly Figure 2, the apparatus is comprised of a mold shell 2, suitably mounted over a casting pit 3, by any of the conventional means. Within the mold shell 2 and extending therebelow, is an embryo ingot 12, comprising a pool of molten metal 5 and solidified casting 5a, the pool 5 extending downwardly and forming a molten metal crater or core within the ingot. Suitably degassed and uxed molten metal is continuously poured into the mold through pouring spout 15 by any of the means commonly used. With regard to the gas content of the incoming molten metal, it has been found highly desirable to have a relatively low gas content which is an inlluencing factor on the casting of sound ingots having good workability. The solidified portion of the ingot rests upon a suitably water cooled block 17, which block in turn is mounted upon a vertically adjustable platen 18. It is to be noted that in the practice of the invention, it may be desirable in certain instances to apply suitable lubricant to the mold surfaces in order to insure against sticking of molten metal to the mold and to insure smooth ingot surfaces.

Means are provided for cooling the mold shell 2, and also for directly cooling the embryo ingot 12 as it emerges from the shell. These means consist of the spray boxes 4, containing the cooling water. These boxes encircle the ingot, and may be of the same construction as that disclosed in Nicholls Patent No. 2,414,269. From these boxes water may be applied around the periphery of the outer surfaces of the mold shell 2, and the surfaces of the embryo ingot emerging therefrom.

Aftixed to each of these spray boxes is a header tank (not shown) connected to the spray box by suitable means for regulating the amount of water head in the boxes.

Located at a predetermined distance below the bottom of the mold shell 2 is a plurality of air jet nozzles or f wipers 13, which project from the air header pipe 9. These nozzles or Wipers are mounted in battery formation in such a manner as to direct air against the sides of an ingot emerging from the mold shell, and to remove the water flowing down the ingots sides. The air wipers are generally positioned with an elevation angle of from to 50 with respect to a horizontal plane normal to the ingot face. The wipers are spaced back from the ingot surface to allow ample clearance between the nozzles and the ingot surface. In most instances, a spacing of from Vs to 11/2 inches has been found to give a satisfactory deflection clearance about the nozzles, thereby avoiding the dropping of water back into the nozzles which would interfere with the otherwise smooth action of the wiper. The air pressure is maintained at a figure suitable for producing a clean line of coolant removal. To avoid the effects of line pressure variations, a pressure regulator may be used on the inlet side of a control valve (not shown) so that the outlet pressure will remain constant for a given predetermined setting of the valve.

The term air jet, as employed herein, is intended to apply to any gas, including nitrogen, the noble gases as well as any other gaseous media. Obviously, air is the most economic gas for such use and is not hazardous in the continuous casting of aluminum and the majority of other metals.

Although other means may be used for completing the removal of the water initially removed by the nozzles, it is contemplated that there be associated with each battery of nozzles a horizontally mounted detiector baille 6. These baffles are successively bent along their lengths so as to form an inclined drain surface 7, a curved portion S fitting about the upper outer periphery of the aforementioned segment of the air header pipe 9, and finally end in a downwardly turned flange 11 located above the tips of the nozzles 13. The air header pipe 9 is comprised of a lower U-shaped portion, to which there is connected by suitable means a separate upper pipe member 10 which is substantially square in plan and which is mounted parallel with the lower U-shaped portion. The air jet nozzles 13 are suitably attached to upper member 10.

Although in the specific form of apparatus disclosed only one tier of nozzles 13 is utilized, it is within the contemplation of the invention to employ multiple sets or tiers of nozzles and batiles which would control the cooling for a considerable distance on the ingots surface.

The water removed from the faces or sides of the ingot is deflected against the bafles 6, whence it finally ows down over the drain surfaces 7 thereof, and into a suitable drain (not shown).

The air header pipe 9 is connected to a suitable source of compressed air supply such as by means of the pipe 19. Associated with this pipe but not shown is an air pressure gauge and a control valve provided with a setting indicator for regulating the pressure of the air being emitted from the nozzles 13.

Each end of the air header pipe 9 may be mounted upon a bracket 20, and L-shaped arms 21 may be connected directly to this bracket. These arms are threadedly mounted upon shafts 22 suitably mounted on the frame 24, said frame also serving to mount the mold shell 2. When shafts 22 are turned by the cranks 22a, they will thereby cause brackets 20 and air header pipe 9 to move upwardly or downwardly, so that the air header pipe 9 and jet nozzles 13 may be drawn up or down with respect to the mold shell 2 and be placed at a greater or smaller distance from the shell, which distance will in turn be governed by the chemical composition of the ingot, the size and shape of the ingot or billet which is being cast, the rate of ingot withdrawal, the rate of flow of coolant, etc. Also, by this means this distance can be adjusted during casting if necessary.

Thus, it will be readily seen that as the ingot is lowered from the mold shell 2, the air streams 23 being emitted from the air nozzles 13, will deflect the water running down along the surfaces of the ingot over batlles 6 and into a suitable drain. These nozzles or wipers 13 are of a design which will deliver a uniform stream of air and can be of a standard type such as shown in Figure 2. They are preferably mounted closely together as shown in Figure t to give complete line coverage for each entire side of the ingot.

Although the air wiper described above, in conjunction with Figures l and 2, is preferred, it is contemplated, within the scope of the invention, to use other types of wipers. For example, certain mechanical wipers can be satisfactorily used, such as those including the use of a ring-like member made of neoprene or other suitable flexible material surrounding the ingot below the mold shell and wherein the inner edge or surface thereof is in rubbing contact with the surfaces of the downwardly moving ingot. In such case the wiper can be held in proper position by suitable means, as by the use of ringlike clamping plate members suspended from the casting housing. Furthermore, it is contemplated, within the scope of this invention that it is not absolutely necessary to the successful operation of the instant invention to utilize the manner of cooling the ingot discussed above wherein liquid coolant is applied to the surface of the ingot as it emerges from the bottom of the mold shell and then is removed at a predetermined level. Instead, this manner of cooling can be replaced with a plurality of jets or nozzles positioned around the ingot periphery and from which fog, atomized water and air, water and steam or other cooling medium is caused to issue in an upwardly direction and impinge upon the ingot surface. The coolant is maintained under sufficient pressure to cause the coolant to be fully spent by being forced into intimate contact with the hot surface of the ingot. The quantity of coolant used per unit time is necessarily less than that needed in the case of the spray box-wiper combination inasmuch as the cooling effect of the coolant is more fully utilized when it is forced under pressure against the hot ingot surface. Also, because of the increased cooling effect, the level of impingement upon the ingot surface will generally be at a level closer to the mold shell than in the case where the spray box is used. The coolant substantially immediately Vaporizes upon contact with the ingot surface and in effect is deflected away from the ingot thereby relieving the necessity of a wiper. In such use of an ingot cooling means, however, the ingot mold shell necessarily has to be provided with a self-contained cooling unit.

Provided within the mold shell 2 and beneath pouring spout l5 is a suitable baille 14. The baille is supported from the top by means of projecting arms which rest on the upper portion of the mold shell while the lower portion of the bate is immersed in the primary molten metal body maintained within the mold. Reference is made particularly to Figures 3 and 4 which show in greater detail the baille 14 used for continuously casting square ingots. The baffle generally comprises vertically extending side portions 30 and bottom portion 3l, the side and bottom portions being connected by intermediate pertion 32. With the bottom portion 31 has been illustrated as being of square configuration and intermediate portion 32 has been illustrated as being of conical contiguration, it will be understood that other bottom shapes may be used as will be more fully discussed hereinafter. located in the side walls of the battle at the corners thereof are leed holes or apertures 33. These apertures are positioned preferably such that they fall on the extremities of the diagonale of the baille and also fall in line with the diagonals of the mold shell as indicated more clearly in Figure l. Projecting outwardly from the battle are a plurality of supporting arms 34. As shown in Figure 2, these arms provide the means for positioning and suspending the baffle within the mold shell. The particular configuration and number of such arms used in any given case is a matter of choice, the primary necessity being that they be sufficient in number and strength to properly support the baille level within the mold shell.

As mentioned hereinbefore, one of the primary ditliculties present in the casting of ingots of relatively massive cross-section is the prefreezing" or freezing back of the molten metal along the periphery of the mold shell. This prefreezing. while present in the casting of all ingots, is particularly prevalent in the casting of ingots having irregular peripheries such as ingots having a square, rectangular or other polygonal crosssection. Such a premature solidication of the metal leads to the defect commonly referred to as cold shuts resulting in a high scrap loss of ingot metal. Prefreezing also may cause the ingot to hang up in the mold shell thereby resulting in surface tears on the ingot, costly shut-down time and further scrap loss. Another major problem present in the casting of ingots is the occurrence of cracking or splitting and shrinkage porosity caused by too great a rate of casting drop and an excessive depth of molten metal crater thereby leading to the creation of thermal strains within the ingot.

As discussed hereinbeforc. it has been tound, accord ing to the instant invention, that the above diiliculties can be considerably reduced or eliminated by properly conv trolling the distribution of molten metal within the primary molten metal body contained within the mold shell. This proper distribution of the metal is brought about by controlling the rate, direction and velocity of flow of the metal to the primary molten metal body in the mold shell. This is accomplished by providing in etect a secondary molten metal body or feeder body of metal between the pouring spout and the primary molten metal body and by means of this secondary metal body controlling the direction, velocity and rate of ow of the molten metal into the primary metal body. The secondary molten metal body is produced by the use of the cup-like baille suitably supported within the mold shell and provided with a plurality of feed holes or apertures adjacent the hase thereof. the size :1nd direction of said apertures controlling the direction, velocity and rate of flow of the molten metal to the primary molten metal body. More particularly, it has been discovered that by directing the llow of motten metal through the plurality of predetermined spaced apertures in the baille beneath the surface of the primary molten metal body and at a predetermined velocity such that a large portion of the metal ows out substantially laterally or at a slight upward angle into contact with or closely adjacent to the cooled mold shell wall and into contact with the upper portion of the solidified ingot shell, there is prevented the build-up of a wall of solid metal in the peripheral surface zone of the primary metal body which inherently will cause prefreezing or freezeback with the result that cold shuts, spill-outs, and surface tears and hanging up of the ingot occur. The initial entry velocity into the primary metal body, which is essential to the practice of the invention, is many times that which is found in the conventional use of prior known bales. Moreover, the prior baffles, which are generally diihed or flat in shape, have not been found practically capable of attaining the necessary velocities of molten metal flow. lt is believed that due to the substantially lateral projection of the molten metal feed to the mold wall and ingot shell that the metal after being caused to flow out laterally toward the wall of the mold shell has had its super heat as well as possibly a portion of its latent heat abstracted therefrom and the cooled metal tends to then flow downward and inward toward the center of the mold beneath the bale where it rapidly solidiiies. This cooling of the molten metal thereby eliminates the formation of a relatively deep metal crater or primary molten metal body along with the inherent adverse cilect upon cracking and shrinkage porosity. In effect, therefore, by means of the present invention, the rate of cooling of the peripheral portion of the metal in the mold shell is being reduced while the rate of cooling of the metal in the central portion of the ingot beneath the baille is being increased thereby resulting in a levelling off of the normal soliditcation curve found in conventional casting practices.

As shown iu Figures l to 2, the preferred battle 14 for the casting of ingots having a substantially square crosssection is generally of cup or dish-shape having a cross-sectional configuration approximating that of the ingot to be cast. In this particular case, it was found that proper distribution of the molten metal Within the mold shell could be had by centering the baille within the mold shell such that the diagonals of thc baille coincided with those of the mold shell and wherein an aperture or feed hole 33 of suitable size was provided at each corner or at the ends of each diagonal oi the baille. By maintaining the proper rate of ow of metal to the baie, the metal was projected out through the corner apertures at such velocity that it was caused to ["low outwardly very close to or in contact with the mold shell and in contact with the upper portion of the solidilied ingot shell at the corner areas which are the rnc-st critical zones from the standpoint of prefreezing" due to the greater area of mold surface for heat abstraction. Although the instant baille 14 is shown to bc of square cross-section, it is to be understood that other designs could be satisfactorily applied as, for example, n spider-shaped baille having a relatively small central cup portion and provided with four diagonally projecting urms which form conduits for the passage of metal outwardly toward the mold shell. irrespective of the specific detail of the particular baille, the critical feature is that the incoming molten metal be caused to ilow outwardly toward the mold shell with suflcient velocity to maintain the periphery of the primary molten metal body in molten condition and thereby prevent tlie build-up of a wall of solidied metal such that preireezing occurs and additionally to remove a predetermined umorent of heat from the metal such that a relatively shallow metal crater is attained.

It has been found advantageous, in thc use of baffles, to provide a conical or inverted frustum shaped bottom thereto to prevent any tendency of the base or bottom of the baille to freeze in with the solidifying ingot. Battle 14, as shown in Figures 3 and 4. is provided with a base or bottom approximating un inverted frustum in shape. By practice of the instant invention the normal solidification line of the metal crater has undergone a considerable levelling thereby in effect raising the line of soliditication in the central portion of the ingot. Where the bottom of the baille is completely ilat adjacent to the base of the vertical extending side portions of the baille, there has been found a tendency for tl e bottom corners to freeze in with the ingot due to the fact that the solidiiication line is too close to the baille corners. Therefore, it has been found preferable to provide the baille bottom with a configuration such that it tends to approximate as near as practical the solidiiication line in the ingot.

Figure 4 of the drawings illustrates another advantageous feature of the invention wherein the baille is provided with a suitable insulated bottom portion. The insulated bottom prevents heat transfer from the secondary molten metal body in the baille to the zone in the ingot located immediately below the baille thereby maintaining the metal in the baille in a highly heated condition while allowing the previously cooled metal beneath the baille to solidify. This arrangement enhances the levelling of the solidication line. As illustrated in Figure 4, the bottom of the baille is made up of a double bottom comprising spaced members 35 and 36. The air space between these members may suillce as insulation or this space may be filled with a suitable insulating material such as alumina. Alternatively, a block of insulation may merely be secured to the bottom of the baille by suitable means.

Where desired, additional holes or apertures may be provided adjacent the base of the baille. As indicated in Figure 3, in dotted lines, pairs of apertures or nozzles 37, 38 may be provided at each corner in addition to the diagonal or corner apertures 33. The apertures 37, 38 may be positioned at an angle to the baille side portions 30 such that metal flowing through them is directed toward that portion of the mold shell adjacent the corners so that the area of the ingot and mold shells in the corners thereof will be thoroughly swept by the hot metal thereby enhancing the eilect of the diagonal apertures. Furthermore, it has been desirable to provide such angular ilow of metal to reduce the amount or extent of heat transmitted from the sides of the baille submerged in the metal head into adjacent metal of the primary metal head. This angular ilow of metal under a predetermined velocity tends to carry the highly heated metal together with the heat given oil by the baille to the mold shell surface. Moreover, in certain instances there may be found a tendency for the molten metal flow to burn the mold shell surface and it has been found that the sweeping action of the angularly disposed nozzles prevents such burning occurring while allowing the projected metal to be in contact or in close relationship with the mold shell for a time suilcient to have the necessary heat abstracted from the metal.

In the casting of ingots having a square or other polygonal cross-section where no apertures are provided for metal ilow at points intermediate the corners or edges thereof, it has been found desirable to utilize a pouring spout having four equally spaced openings at the lower end thereof. The openings should be at an angle to the longitudinal axis of the spout and each opening should be directed at a vertical extending side portion of the bafile and at the middle or intermediate part of the side portions. Such a ilow of metal will tend to keep the intermediate side portions of the baille in a sufllciently heated condition to prevent any tendency toward freezing-in of the baille sides to the mold shell.

In the design of a baille for any given size and shape of ingot, only a nominal amount of experimentation is necessary to determine the proper size and placement of the apertures. It is to be noted, however, that where the apertures are made too small, the molten metal tends to freeze and clog the apertures, while if the apertures are made too large, the velocity of ilow of the metal is insuilicient to give the necessary force to the metal required to move it to the solidiiled ingot shell and the chilled face or surface of the mold shell. It has been determined that for the casting of ingots of relatively massive size as large as 32" in diameter or over, regardless of the cross-sectional shape whether it be round, polygonal, etc., that apertures ranging from about 1A" to 5A" in diameter have been found satisfactory. It is preferred, however, to use an aperture size on the order of from 3A" to 1/2 in diameter. The larger the size of the aperture used, the closer should the baille side portions be located to the mold shell to compensate for the lack of force or velocity. Care should be exercised that the size of the opening does not require such a reduced spacing between the baille and mold shell that freezingin of the baille takes place. By proper selection of aperture size this diiliculty is readily corrected. Although round apertures have been specifically disclosed and discussed, it will be obvious that various configurations can be satisfactorily used.

Figures 5 and 6 illustrate a baille design for use 1n the casting of ingots having a circular cross-sectional shape. As shown, the baille comprises a vertical extending annulus 40 and a bottom 41, said annulus being connected to the bottom by means of intermediate portion 42. As in the case of the square baille shown in Figures 3 and 4, the circular baille preferably has the bottom shaped similar to the inverted frustum of a cone to approximate the solidiiication line of the ingot being cast. Projecting outwardly from the main baille body are a plurality of arms 44 for suitably supporting the baille within the mold shell. A plurality of nozzles 43 are mounted on annulus 40 and these nozzles project at an angle thereto. This baille, as in Figure 4, may also be provided with an insulated bottom for the same reasons set forth hereinbefore.

The nozzles 43 are preferably placed at such an angle with regard to the main body of the baille that the ilow of molten metal toward the mold the ingot shells take a substantially tangential path giving rise to a sweeping action. By means of this direction of ilow of the molten metal from the baille there is attained a uniform distribution of hot metal to the mold and ingot shells thereby preventing any tendency of prefreezing of metal along the mold shell at points which would occur in the case where there has been insuicient hot metal contact. Moreover, this angular ilow of metal reduces the tendency toward loss of heat from or uneven temperatures in the area adjacent the mold shell which would tend to result were use made of spaced nozzles or apertures directed radially outward from the baille thereby giving rise to uneven heat abstraction around the periphery of the mold shell.

It is to be understood, with regard to the number and position of the apertures or nozzles in any given case, that these factors will necessarily be determined by such things as the size, shape, and composition of the ingot being cast. For example, it has been one of the practices to cast certain sizes of square ingots using a square baille with only four apertures, one in each corner, as illustrated in Figures l to 4. Where the cross-section of the square ingot becomes suiliciently massive it requires the provision of additional apertures or nozzles spaced between the corner apertures.

In the casting of ingots of relatively massive crosssection by means of the instant invention, it has also been determined that the rate of ilow of molten metal from the pouring spout into the baille and mold shell is an influencing factor on the casting of satisfactory ingots. The rate of metal ilow in conjunction with the baille design determines the velocity of the metal passing out of the apertures or nozzles into the space between the baille and the mold shell. Although the rate of metal ilow may extend over a considerable range with satisfactory results, other casting factors remaining constant, it has been found preferable to maintain the rate of ilow of metal from not substantially below 300 cubic inches per minute to not inches per minute. This rate of metal ilow not only corisubstantially in excess of 900 cubic trols the velocity of the metal issuing from the baille in conjunction with the feed apertures or nozzles, but it also necessarily determines the rate of ingot withdrawal from the mold. In other words, for any given rate of ilow the larger the cross-sectional area of the ingot the smaller will be the rate of ingot withdrawal. Although the rate of molten metal ilow may be constant from one ingot size to another, the velocity of llow of the metal from the baille apertures or nozzles may vary depending upon the number and size of the apertures. It has been found desirable generally in the casting of ingots having corners or edges to maintain a higher velocity of metal to these critical zones than in the case of a circular ingot where all the portions of the surface are cooling at substantially the same rate. As specific examples of the above, it was found that in using a ilow rate of 600 cubic inches per minute in the casting of 18" by 18" square and 32" diameter round 75S aluminum alloy ingots that in the 18" by 18" ingot, the drop rate was on the order of 2" per minute and the velocity of the metal from the corner bale apertures was on the order of 760 inches per minute while in the case of the 32 diameter ingot, the drop rate was on the order of 3/4" per minute and the velocity of the metal ilowing from the apertures was on the order of 330 inches per minute. It is to be understood that the velocity of the metal ilow from the baille apertures may vary over a wide range depending upon the spacing of the apertures from the mold shell, and the number and size of apertures provided. As set forth hereinbefore, it is important to have the requisite velocity and direction of metal ilow to move the metal out toward the mold and ingot shells or the peripheral zones of the metal head in order to prevent prefreezing" and the formation of cold shuts and surface tears and to remove suilicient heat from the molten metal such that upon continued flow of the metal downward and inward toward the central portion of the ingot the metal will rapidly freeze without the formation of a deep molten metal crater.

With further reference to Figure 2, it will be noted that the secondary metal body within the baille has been illustrated as being above that of the primary metal head in the mold shell. Although it is not necessary to the successful operation of the invention, it is preferred to maintain the surface level of the secondary metal body in the baille from about V2" to 1" above the surface level of the primary metal body in the mold shell. It has been found that by the use of this increased head in the baille, better control of the feeding characteristics of the molten metal to the mold shell can be attained. Moreover, by the use of the relatively small secondary metal body in the baille, any small change in the rate of ilow of metal to the baille is quickly noticeable in change of head level making rate of llow changes quickly detectable and controllable.

Accordingly, by controlling the distribution of the metal into the primary metal body in the mold shell, or in other words, by properly regulating the rate of flow of metal into the mold shell such that it is on the order of 300 to 900 cubic inches per minute and by causing the molten metal to originally travel outwardly toward the mold shell at a velocity sutlicient to maintain the periphery of the metal head in highly heated condition, in addition to the prior known feature of controlling the rate of heat abstraction from the solidified ingot such that the surface temperature of the ingot will be maintained at a temperature of not substantially below about 300 F. and preferably is maintained at a temperature of from 400 to 650 F., below the level of coolant removal during the remainder of the casting operation sound ingots of relatively massive cross-section can now be successfully cast by the continuous process with consistently reproducible results and with a minimum of control necessary. The ingots produced by practice of the invention are free or substantially free of the occurrence of cold shuts, center splits and edge cracks. In addition, the occurrence of hanging-up of these large ingots within the mold shell due to solidification of metal on the mold shell and freezing-back" of the metal has been eliminated. Moreover, the ingots possess a relatively tine grain structure, have low shrinkage porosity and possess a relatively ne size and distribution of alloying constituents.

Satisfactory results have been obtained in continuously casting 18" by 18" square ingots of 75S high strength aluminum alloy comprising about 1.6% copper, 0.1% silicon, 2.5% magnesium, 0.4% iron, 5.8% zinc, 0.05% titanium, balance aluminum. The ingot lengths varied from about to 100 inches. The pouring temperature of the molten metal was in the range of from about 1225 to 1300* F., and the height of the primary molten metal body above the base of the mold shell was about 3 to 3V1". The baille was generally of square cross-section measuring approximately 11 inches on a side and having an inverted frustum-like bottom section. Four feed holes or apertures were used, one aperture being provided at each corner of the battle adjacent the bottom thereof and each aperture being about V2" in diameter. The secondary metal head (in baille) was maintained at a level about V2" above that of the primary metal head. The rate of ingot withdrawal was about 2" per minute and the rate of metal flow was on the order of 650 cubic inches per minute. The coolant was removed from the ingot surfaces by air wipers at a level of from about 4 to 7 inches below the base of the mold shell and the stabilized surface temperature of the solidified ingots below the level of coolant removal varied from about 440 to 650 F.

Other examples of the invention include the continuous casting of 32" diameter 75S aluminum alloy ingots. The ingot length was on the order of The pouring temperature of the molten metal was in the range of from about 1270" to 1310 F. and the height of the primary molten metal body above the base of the mold shell was about 3% to 4V2 inches. The baille was generally of circular cross-section measuring approximately 20 in diameter and having an inverted frustum-like bottom section. Twelve spaced nozzles or feeding apertures were provided on the baille, each being approximately V2" inside diameter and being inclined at an angle of about 45 to the baille surface. The secondary metal head (in baille) was maintained at a level about l/t to 3A" above that of the primary metal head. The rate of ingot withdrawal van'ed from about 3/21" to 1" per minute and the rate of metal flow varied from about 600 to 800 cubic inches per minute. The coolant was removed from the ingot surface by means of air wipers at a level of about 81/2 inches below the base of the mold shell and the stabilized surface temperature of the ingots below the level of coolant removal varied from about 440 to 570 F.

It will thus be seen that by proper selection of the rate of metal flow and proper distribution of the metal within the mold shell, in addition to proper control of the rate of heat abstraction from the lower portion of the ingot, sound ingots of massive cross-section having various con gurations such as round, square, or other polygonal shape can now be continuously cast in a highly successful manner with a minimum of scrap loss and requiring a minimum of control. The instant invention has particular application to high strength aluminum alloys such as 75S as well as to other aluminum alloys such as 14S, 17S, 24S, etc.

In the event that ingots cast by the practice of the instant invention are to be subjected to a hot working operation, such as forging, a relatively short time after the casting thereof, it may be desirable to place the cast ingots within a suitable insulated container to reduce the rate of cooling below the stabilized surface temperature. Such a procedure not only reduces the time period that the ingots need be in a preheating furnace prior to hot working, but in the case of casting relatively massive ingots it eliminates the formation of stress cracks which might tend to occur because of an excessive rate of preheating giving rise to large temperature differentials between the surface and core portions of the ingot.

It will be understood that various changes, omissions and additions may be made to this invention without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

l. In the continuous casting of light metals, wherein molten metal is continuously fed to a relatively short open mold shell containing a molten metal body, is partially cooled therein to form an outer Shell of solidified metal, and a cooling medium is applied to the casting emerging from said mold shell to rapidly cool the casting, the improvement which comprises directing the incoming molten metal feed into a secondary molten metal body which is contained partially within the first-mentioned molten metal body, the surface level of said secondary molten metal body being maintained above that of the first-mentioned molten metal body, directing substantially all of the metal in said secondary molten metal body to llow outwardly into said first-mentioned molten metal body beneath the surface thereof and in a direction and at a velocity such that the iiow of metal is substantially tangential with respect to the retaining surfaces for said first-mentioned molten metal body and the flowing metal moves into substantial sweeping contact with said retaining surfaces whereby a portion of the heat is abstracted therefrom, and thereafter the partially cooled molten metal flows downward and inward toward the central portion of said firstmentioned molten metal body at a reduced velocity where said partially cooled metal rapidly freezes.

2. A method according to claim l wherein said outward iiow of molten metal is relatively close to the surface of the iirst-mentioned molten metal body.

3. In the continuous casting of light metals, wherein molten metal is continuously fed to an open mold shell containing a molten metal body, is partially cooled therein to form an outer shell of solidified metal, a cooling medium is applied to the casting emerging from said mold shell to rapidly cool the casting, and wherein the cooling medium is subsequently effectively removed from the surface of the casting such that the surface of the casting will be maintained at a temperature of not substantially below about 300 F. during the remainder of the casting operation, the improvement which comprises directing the incoming molten metal feed into a secondary molten metal body which is contained partially within the rstmentioned molten metal body, the surface level of said secondary molten metal body being maintained above that of the first-mentioned molten metal body, directing substantially all of the metal in said secondary molten metal body to ow outwardly into said first-mentioned molten metal body beneath the surface thereof and in a direction and at a velocity such that the ow of metal is substantially tangential with respect to the retaining surfaces for said first-mentioned molten metal body and the flowing metal moves into substantial sweeping contact with said retaining surfaces whereby a portion of the heat is abstracted therefrom, and thereafter the partially cooled molten metal flows downward and inward toward the central portion of said first-mentioned molten metal body at a reduced velocity where said partially cooled metal rapidly freezes.

4. A method according to claim 3 wherein the outwardly directed molten metal flow is substantially parallel with, and relatively close to, the surface of said iirstmentioned molten metal body.

5. A method according to claim 3 wherein the rate of molten metal feed to the mold shell is from about 300 to about 900 cubic inches per minute.

6. In the continuous casting of light metals, wherein molten metal is continuously fed to an open mold shell containing a body of molten metal, is partially cooled therein to form an outer shell of solidified metal, and a cooling medium is applied to the casting emerging from said mold shell to rapidly cool the casting, the improvement which comprises directing the incoming molten metal feed outwardly in the form of a plurality of streams in such direction and at such velocity that the flow of metal is substantially tangential with respect to the retaining surfaces for said molten metal body and the molten metal flows to the outer zone of the molten metal body in substantial sweeping contact with the retaining surfaces therefor whereby a portion of the heat is abstracted therefrom, and thereafter the partially cooled molten metal flows inward toward the central portion of said molten metal body at a reduced velocity where said partially cooled metal rapidly freezes.

7. A method of continuously casting metal comprising the steps of feeding molten metal into the central portion of an open mold shell containing body of molten metal, applying a coolant to the outer surface of said mold shell to form an outer shell of solidied metal therein, directing substantially all of the incoming molten metal feed outwardly beneath the surface of said body of molten metal in a direction and at a velocity such that the flow of metal is substantially tangential with respect to the outer shell of solidified metal and the flowing metal moves to the outer zone of said molten metal body in substantial sweeping contact with the upper portion of said solidified ingot shell whereby the molten metal is partially cooled, and thereafter the partially cooled metal ilows inward at a reduced velocity toward the central portion of said molten metal body where said partially cooled and relatively quiet metal solidies, and applying a cooling medium to the surface of the casting emerging from said mold shell.

8. A method according to claim 7 wherein the incoming molten metal feed is directed outwardly in the form of a plurality of streams.

9. A method according to claim 8 wherein said plurality of streams are relatively close to the surface of said molten metal body.

l0. The improvement in an apparatus for the continuous casting of metal comprising the combination of an open mold shell adapted to contain a body of molten metal, means for cooling said mold shell, means for cooling an embryo casting emerging from said mold shell, molten metal delivery means adapted to feed molten metal into said mold shell, bafe means positioned in said mold shell beneath said delivery means and adapted to receive molten metal therefrom, said bafe means comprising a container having an imperforate bottom portion and being provided with a plurality of directional feed apertures adjacent the bottom portion, said apertures being positioned at substantially the same level with respect to said mold shell and being positioned at an angle in relation to said mold shell such that the flow of molten metal passing out of said baffle through said apertures will be substantially tangential with respect to the retaining surfaces for said molten metal body.

1l. An apparatus according to claim l0 wherein said directional feed apertures are in the form of nozzles.

l2. An apparatus according to claim l0 wherein said container is substantially square in plan, said mold shell is substantially square in plan, and wherein the container is provided with a feed aperture at each corner of said container such that the apertures are in line with the diagonals of said container.

References Cited in the le of this patent UNITED STATES PATENTS 1,385,595 Van Ranst July 26, 1921 2,224,303 Junghans Dec. 10, 1940 2,243,425 Junghans May 27, i941 (Other references on following page) 15 UNITED STATES PATENTS Webster July 14. 1942 Ennor Nov. 3, 1942 FOREIGN PATENTS Canada July 22, 1952 16 France Mar. 29, 1943 France Oct. 30, 1944 Germany Aug. 6, 1951 Germany July 7, 1952 Germany July 24, 1952 

10. THE IMPROVEMENT IN AN APPARATUS FOR THE CONTINUOUS CASTING OF METAL COMPRISING THE COMBINATION OF AN OPEN MOLD SHELL ADAPTED TO CONTAIN A BODY OF MOLTEN METAL, MEANS FOR COOLING SAID MOLD SHELL, MEANS FOR COOLING AN EMBRYO CASTING EMERGING FROM SAID MOLD SHELL, MOLTEN METAL DELIVERY MEANS ADAPTED TO FEED MOLTEN METAL INTO SAID MOLD SHELL, BAFFLE MEANS POSITIONED IN SAID MOLD SHELL BENEATH SAID DELIVERY MEANS AND ADAPTED TO RECEIVE MOLTEN METAL THEREFROM, SAID BAFFLE MEANS COMPRISING A CONTAINER HAVING AN IMPERFORATE BOTTOM PORTION AND BEING PROVIDED WITH A PLURALITY OF DIRECTIONAL FEED APERTURES ADJACENT THE BOTTOM PORTION, SAID APERTURES BEING POSITIONED AT SUBSTATIALLY THE SAME LEVEL WITH RESPECT TO SAID MOLD SHELL AND BEING POSITIONED AT AN ANGLE IN RELATION TO SAID MOLD SHELL SUCH THAT THE FLOW OF MOLTEN METAL PASSING OUT OF SAID BAFFLE THROUGH SAID APERTURES WILL BE SUBSTANTIALLY TANGENTIAL WITH RESPECT TO THE RETAINING SURFACES FOR SAID MOLTEN METAL BODY. 